S64 Professor Breithaupt on Hyahsiderite and Trachylyk. 



celain Manufacture at Meissen, has, with an economical view, 

 undertaken a chemical examination of the Orthoclases, from Aue 

 near Schneeberg. He finds, that, in those varieties which are the 

 least decomposed, there is a smaller quantity of potash and more 

 alumina, than in the fresh or unaltered varieties ; while the more 

 completely decomposed afford no potash, but more alumina. 

 These examples, we think, are sufficient to prove, that a mineral 

 can only be considered as a new species, when it possesses essen- 

 tial differences from all known species, and can be examined in a 

 fresh state. It also leads to erroneous views as to composition, if 

 the mineral is examined, not in a fresh, but in a decomposed con- 

 dition. 



III. Trachylyte, probably a New Mineral Species. 



Ix Characters of Trachylyte. — Colours velvet, brownish and 

 greenish black ; occurs massive and in plates ; lustre vitreous, 

 sometimes inclining to resinous ; fracture generally small con- 

 choidal, seldom uneven ; no trace of cleavage ; fragments sharp 

 edged ; opaque ; streak dark ash grey ; easily frangible ; hard- 

 ness = 8.5. (between orthoclase and quartz) specific gravity 

 = 2.50 to 2.54. 



2. Observations. — It resembles Obsidian more than any other 

 mineral, but is distinguished from it by streak, greater specific 

 gravity, &c. and certainly by its chemical composition. Both 

 minerals appear members of the same genus. In colour, lustre, 

 and fracture, the Trachylyts approaches very near to Gadolinite. 

 Its appearance before the blowpipe is remarkable ; it melts in- 

 stantaneously with intumescence, into a brown and sometimes 

 vesicular slag. Hence its name, which refers to its rapid melt- 

 ing. 



Hitherto this mineral has only been found at Siisebiihl, be- 

 tween Dransfeld and Gottingen, where it occurs in small massive 

 and plate formed masses, imbedded in basalt and wacke. It 

 has been confounded with conchoidal Augite * ; but true con- 

 choidal Augite is sufficiendy distinguished from it, by specific 

 gravity, which, in that of the Rhon, is 3.474, not to mention 

 that it always exhibits traces of a cleavage in the direction of a 

 primary rhombic prism. 



• Hausmann's Handbuch der Mineralogie, s. 690. 



